The invention presented herein relates to an exposure control that is usable with imaging apparatus for controlling the amount of light energy from a light source wherein the light source is directed to an image which with optics provides a focused light image to a light responsive member and, in particular, to such an exposure control wherein a portion of the focused light image is received by a photocell, the output of which is used to adjust the on time for the light source to compensate for changes in the light source output and the image background density.
various exposure controls have been devised for imaging equipment using a photocell position to receive a portion of the light image to provide a signal that is used to alter the light exposure to which a light responsive member is subjected to compensate for changes in the light source output and the background density of the image used to produce the light image. More flexibility for placement of the photocell is provided if the photocell is not positioned within the path of the light image. It is also desirable to use a significant portion of the focused light image so a better measure of the image background density will be obtained. This latter goal is sought in various prior art arrangements by the use of more than one photocell and using an average of the responses from the photocells for control purposes. A prescan of the light image has also been used to provide a measure of the image background density for use with an exposure control. The prior art arrangements do not show how a measure of the light image for a fairly representative area of the light image can be obtained with a single photocell when a full frame exposure is used.